# 3.9 Exercises

Assume diodes are silicon unless stated otherwise

## Analysis Problems

1. Determine β if α = 0.99
2. Determine α if β = 200
3. Determine the currents for the circuit of Figure 3.9.1 if VBB = 5 V, VCC = 20 V,
RB = 200 kΩ, RC = 2 kΩ, β = 100.
4. Determine the transistor voltages for the circuit of Figure 3.9.1 if VBB = 5 V, VCC = 20 V,
RB = 200 kΩ, RC = 2 kΩ, β = 200.

5. Determine the LED current in the circuit of Figure 3.9.2 if Vlogic = 5 V, VCC  = 5 V,
VLED = 2.1 V, RB = 3.6 kΩ, RC = 270 Ω, β = 100.
6. Determine the LED current in the circuit of Figure 3.9.2 if Vlogic = 0 V, VCC = 5 V,
VLED = 2.1 V, RB = 3.6 kΩ, RC = 270 Ω, β = 100.
7. Determine the LED current in the circuit of Figure 3.9.3 if Vlogic = 5 V, VEE = 5 V,
VLED = 2.2 V, RB = 2.7 kΩ, RC = 220 Ω, β = 100.

8. Determine the LED current in the circuit of Figure 3.9.3 if Vlogic = 0 V, VEE = 5 V,
VLED = 2.2 V, RB = 2.7 kΩ, RC = 220 Ω, β = 100.
9. Determine the LED current in the circuit of Figure 3.9.4 if Vlogic = 3.6 V, VCC = 10 V,
VLED = 2.3 V, RE = 270 Ω, β = 200.

10. Determine the LED current in the circuit of Figure 3.9.4. Vlogic = 0 V, VCC = 10 V,
VLED = 2.3 V, RE = 270 Ω, β = 200.
11. Using the 2N3904 data sheet, determine VCE(sat) if IC = 30 mA and IB = 1mA.
12. Using the 2N3904 data sheet, determine the percent change in β if IC = 10 mA and the temperature rises from 25°C to 125°C.
13. Using the 2N3904 data sheet, determine the percent change in β if IC = 40 mA and the temperature drops from 25°C to −55°C.

## Design Problems

1. Using Figure 3.9.1, determine a value for RB to set IC to 5 mA if VBB = 5 V, VCC = 25 V,
RC = 2 kΩ, β = 100.
2. Using Figure 3.9.1, determine a value for RC to set VCE to 6 V if VBB = 10 V, VCC = 25 V,
RB = 330 kΩ, β = 200.
3. For the circuit of Figure 3.9.2, determine a value for RC to set the LED current to 15 mA. Vlogic = 5 V, VCC =5 V, VLED = 1.6 V, RB = 3.3 kΩ.
4. For the circuit of Figure 3.9.3, determine a value for RC to set the LED current to 20 mA. Vlogic = 0 V, VEE = 5 V, VLED = 2.0 V, RB = 2.7 kΩ.
5. For the circuit of Figure 3.9.4, determine a value for RE to set the LED current to 25 mA. Vlogic = 5 V, VCC = 9 V, VLED = 2.8V.

## Challenge Problems

1. Determine the maximum and minimum values for IC in the circuit of Figure 3.9.1 if all resistors have a 10% tolerance and β = ranges from 100 to 200.
VBB =5 V, VCC = 20 V, RB = 200 kΩ, RC = 2 kΩ.
2. Derive and draw a PNP non-saturating LED driver circuit.

## Computer Simulation Problems

1. Simulate the circuit of Problem 3.
2. Simulate the circuit of Problem 5.
3. Simulate the circuit of Problem 7.
4. Verify the design of Problem 14 using a simulator.